Modems. Chapter 17. Modems are little devices to use the telephone to talk to other computers. Modem is an abbreviation for Modulator/ Demodulator Modems can be internal or external. Basic Knowledge. Modem Signals.
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Modems take analog signals and convert them into digital signals and vice versa.
The data that goes into the modem is called serial communication and is a series of 0’s and 1’s. This data is converted into bytes via the UART(Universal Asynchronous Receiver/Transmitter) so CPU’s can understand information
There are 2 ways of “chopping up” the incoming signals
The data is “chopped up” into 7 or 8 bit packets. 8-bit is most common
Each Packet starts with a start bit that tells the receiving modem that it is the beginning of a piece of information and it always is zero and ends with a stop bit that tells the receiver the packet is over.
Asynchronous communication packets have an optional parity bit used for error detection. Parity bits are rare
Asynchronous packet settings are described in a particular order: data bits, parity type, then stop bits.
Example: If a system uses 8 data bits, no parity, and 1 stop bit, you’d say 8-N-1.
It takes parallel information from data buses and makes it serial information to be sent out to a modem.
It’s important to know what type of UART is in your COM ports. You can find out the type by checking the diagnostics tab/ More Info button under the Modems applet in the control panel under windows 9x. In Windows 2000 use the Phone and Modem Options applet.